This project will test the following specific aims: 1) the effects of high-fat (HF) and high-sucrose (HS) diets on glucose uptake, hepatic glucose cycling and hepatic glycogen synthesis using new methods. 2) Effects of these diets on hepatic fatty acid uptake, oxidation and gluconeogenesis, and the regulatory steps involved. 3) The role of increased Na K ATPase activity on the metabolism of fat and glucose. 4) Contribution of microsomal glucose-6 phosphatase to hepatic insulin resistance. Hepatic glucose uptake will be measured by euglycemic hyperinsulinemic clamp, accompanied by mesenteric glucose infusion. Glucose cycling will be measured using 6-3H glucose and 2-3H-glucose. Fatty acid oxidation will be measured as C02 production from dehydroxyacetone (DHA) will also be measured both in the presence and absence of ouabain. To test whether the increased N K ATPase activity is due to increased synthesis of diacylglycerol and consequently activation of protein kinase C, synthesis of neutral and phospholipids from U-14C-glucose and membrane bound PKC activity will be measured. Finally, to explain the decreased Km of G-6Pase for G6P during HS diet, and increased Vmax during HF diet, kinetics of this enzyme will be measured in the intact and disrupted microsomes.